The multi-channel ion Doppler spectroscopic (M-IDS) system using a fast camera as detectors has been newly developed to measure the spatial profiles of impurity spectral line emissions from plasmas. The M-IDS system developed with 8 viewing chords is characterized by the simplest optical systems, a fast sampling frequency, high number of shooting and a low crosstalk of 3.5% on each chord. In order to verify the usefulness and reliability of the M-IDS system, we have applied it for the start-up plasma produced in the Helicity Injected Spherical Torus (HIST) device. Resultantly, we have successfully measured the radial profiles of Doppler ion temperature T_i.D and Doppler ion velocity v_i.D of the plasma with a good Gaussian fitting. However, we have found that the sampling frequency is upper limited by 25 kHz because the signal detected with a faster frequency from the CIII impurity line emission is too weak to be analyzed, so that the sensitivity of the total system needs to be improved.

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Thermal barrier coating (TBC) is applied to high temperature components in gas turbines. The thermally grown oxide (TGO) layer, which forms at the interface between the topcoat and the bondcoat, is an origin of topcoat damage, which can lead to delamination of the topcoat. In order to detect the TGO layer in in-service components, a portable detection system based on photoluminesence was developed. The system consisits of a compact, continuous wave Nd:YAG laser of wavelength 532 nm to excite Cr³⁺ included as an impurity in Al₂O₃, and a compact spectrometer with a 2-D CCD array for enhanced sensitivity to detect the photoluminescence from Cr³⁺ at 694.3 nm (R₁) and 692.9 nm (R₂). An optical probe is used to illuminate the specimen with laser light and to collect the photoluminescence. The probing region is a circle of diameter 5 mm. The optical probe is coupled to the main body by an optical fiber, which allows flexibility to match specimens with curved surfaces or complex structures. The system performance was tested using TBC specimens heated at 1000°C and 1100°C, and an as-sprayed, unheated TBC specimen. Photoluminescence (R₁, R₂) was observed from heated specimens and was not observed from the unheated specimen, and agreed with previous measurement results. This system can be used for screening tests of topcoat delamination inspection, since delamination is likely to occur at locations where the TGO layer has grown.

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We investigated the decisive factors which affect partial discharge inception voltage (PDIV) fluctuation between the coil wires under a sinusoidal voltage by using a rectangular wire motor. As the result, we found that PDIV under low humidity fluctuates by the surface charge, and PDIV under high humidity varies transitionally with the surface conductivity activated by pre-discharge. From these analyses, we proposed the measurement method of PDIV with a low fluctuation and transition for the rectangular wire motors, which will be optimized by environmental humidity, pre-discharge condition and measuring frequency.

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Based on the mechanism of surface flashover development in vacuum, we have investigated that the surface flashover can be suppressed by the increase in electric field perpendicular to the insulator surface. In this study, we clarified the suppression conditions of surface flashover in terms of the transient surface charge and the effective secondary electron emission coefficient along the insulator surface.

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The discharge current path and performance of a steady-state, self-field magnetoplasmadynamic (MPD) thruster using argon propellant have been examined under the assumption of temperature distributions on the cathode by axisymmetry two-dimensional magnetohydrodynamic (MHD) flow simulation with electrode sheath model as the boundary condition. The discharge current path in the thruster is affected not only by the Hall effect but also by the distribution of thermionic emission from the cathode. When the cathode temperature is decreased from the tip to the root, the discharge current shifts to the cathode tip, which mitigates the current concentration toward the cathode root due to the Hall effect. Then, the thrust is increased as well as the input power, and the thrust efficiency is almost the same as that under the constant temperature distribution on the cathode.

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For a 10N-class, steady-state, self-field magnetoplasmadynamic (MPD) thruster using hydrogen as the propellant, the distribution of discharge current path has been investigated by means of axisymmetry two-dimensional magnetohydrodynamic (MHD) flow simulation including an electrode sheath model with cathode temperature distributions. The discharge current path concentrates in the downstream region of the thruster, particularly on the anode edge and the cathode tip, because the ionization of hydrogen occurs after the dissociation. This feature is so dominant that the cathode sheath voltage is determined mainly by the temperature at the cathode tip and the discharge current path is hardly affected by the temperature gradient of the cathode. These characteristics are quite different from those for argon MPD thruster.

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A magnetized coaxial plasma gun (MCPG) device at Univ. of Hyogo was used as a simulation facility for pulse heat loads such as ELMs (Edge Localized Modes) onto plasma-facing materials in magnetically confined fusion devices. In the present study, characterization of the compact toroid (CT) plasmas produced by the MCPG device was performed. Dependences of the CT plasma parameters of line-averaged electron density, ion temperature and flow velocity on the gun discharge voltage and the bias magnetic flux were measured. As a result, it was observed that the pulse length, the line-averaged electron density, and the ion temperature and flow velocity were approximately 200 µs, approximately 6×10²¹ m^-3, approximately 30 eV, and approximately 50 km s^-1, respectively. The surface energy density measured with a tungsten calorimeter was approximately 0.4 MJ m^-2. Thus, it was shown that the ELM-like pulsed plasma heat loads with the energy density and the pulsed length predicted in the ITER divertor can be produced using the MCPG device.

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We studied usefulness of a frequency accelerated aging test by paying attention to the number of partial discharge (PD) pulses and the accumulated PD charges per a cycle of frequency of applied voltage. The results shows that a frequency accelerated aging test is useful when the accumulated PD charges per a cycle of frequency of applied voltage with higher than PD inception voltage are the almost same as that at a commercial frequency of 60 Hz. If applied frequency is 1 kHz, an accelerated aging test with 16.6 times faster than that for 60 Hz can be achieved.

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